The influece of dopaminergic and glutamatergic inputs on the activity of GABA neurons in various areas of the brain has been studied. Electrical stimulation of the substantia nigra and A10 area was used to obtain an enhanced dopaminergic activity in N. caudatus and N. accumbens. Ablation of the cortex was employed to suppress glutamatergic input into N. caudatus. The activity of GABAergic neurons was assessed by measuring the turnover rate of GABA using a gas chromatographic-mass spectrometric technique. In one experiment, a similar technique was employed to study the activity of cholinergic neurons. Our results show that in N. accumbens, but not in N. caudatus, dopamine directly inhibits GABA neurons. In N. caudatus glutamatergic fibers originating in the cortex stimulate the activity of GABA and acetylcholine neurons.